Wearable displays have received broad attention in recent years after smart phones became popular and are well accepted by the market. Wearable displays provide the benefits of hands free operation as well as showing the images to the person who wears the display at a distance same as regular sight. Because of these advantages, there are tremendous needs for wearable displays. However, the conventional near eye displays such as Head Mount Display, Head up Display and Eye Glass Type Display have not provided satisfied wearable display solutions to the viewers, because these conventional devices are often too heavy, too large, and too dark. Furthermore, these conventional wearable displays often have low resolution and many of them do not provide a see-through view and are mostly expensive and can only display small size of images. Therefore, there are urgent needs for providing wearable display devices that are light, small, bright, having high resolution with see-through viewing optical path. It is further desirable that the new wearable devices are inexpensive that can display large image and can be putted on in a stealthy manner without being detected by others that the person is wearing such a wearable device. Display systems implemented with LED and Laser light sources usually have a technical problem with uneven distribution of light intensity and a homogenizer is typically required for the display systems to provide uniform brightness of image. Three separate color light sources require to combine into a single light beam before projecting onto a display device. Enabling a compact eye-glass type display requires a very small system having both homogenizer and combiner. Several systems are proposed in the past.
As shown in FIG. 1, Takeda et al. disclosed in U.S. Pat. No. 8,711,487 an eye glass type display system that implements see-through capability with a wave guide and a half-mirror. This system incorporates a transmissive LCD as a display and the illumination system is a backlight light-guide that diffuses the light from the light source. This system is suitable for transmissive LCD, but not necessarily suitable for other display devices such as LCOS and DMD.
As shown in FIG. 2 and FIG. 2A, Takahashi et al. disclosed in US Patent Application Publication US2013/0021581 an illuminator and a display for miniaturization. The system comprises multi-color light sources such as LED and Laser (11) with micro-lenses (116) to collimate, dichroic mirrors (117) to combine light beams as shown in FIG. 2A and a polarized beam splitter (PBS, 16) arranged in perpendicular direction from LCOS (17). If this is used for an eye-glass display and embedded in a temple of glasses, this illuminator will stick out of the temple of glasses.
As shown in FIG. 3, Katsumata et al. disclosed in JP2013-195603 a Planar Lightwave Circuit (PLC). A beam from a laser diode is lead into a light-wave guide and the light energy in a light-wave can be transferred to an adjacent light-wave guide in a certain condition. This method is suitable for a combiner of laser light sources and has a great potential, although it requires further study prior to high volume commercialization.
This invention presents a practical solutions of an illuminator applicable to eye-glass display